Air pick-off for sensitive instruments



Aug. 18, 11.942.'

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atented Aug. i8, 1942 UNirs-n .STATS Ain Prox-arr Fon sensrrrvn ms'rgnrJMENrs William M. Harcum, Brooklyn, Y., assigner to Sperry Gyroscope Company, Inc., Brooklyn, N. Y., a. corporation of New York Application June 1, 1938, Serial No.. 211,307

'z claims. (ci. 121-41) This invention relates to differential sir now pick-oil? devices for sensitive instruments vin which it is importantv that no torque be exerted.'

on the latter; My invention has special application tothe vacuum or negative pressure type of pick-off wherein air is continuously exhausted from the enclosure containing the pick-off device or devices and dilerentially ows into the enclosure through opposite ports which are oppositely closed and opened upon relative displaceis to overcome the foregoing deficiency in the present vacuum systems by providing a means for ment of the sensitive device and the follow-up device or fixed part of the craft. Such devices have become quite common in the art of automatic pilots for airplanes, for example, being shown in the prior patent to Sperry, Carlson and Bates No. 1,992,970 dated March 5, 1935. 'A more recent example is shown inthe copending application of Theodore W, Kenyon and Stephen J. Zand, now Patent No. 2,210,916, for Automatic I pilot for dirigible craft, dated August 13, 19.40,

and it is to this type of pilot that my invention isshown applied.

In the differential flow system it is necessary to provide leaks either at the relay or other control device, or in the line between the relay and the pick-ol intake port. For instance, in the' aforesaid prior patent of Kenyon and Zand; leaks are shown in the air chambers of 'the relay valve and also-in theair chambers of the pick-oir device. 'I'he purpose of such leaks is to create the 'necessary ow of air toward both pick-off ports so as to produce the diiferential pressure in the vtwo lines when the ports are diierentially opened and closed. Such leaks, however, are themselves the cause of an inherent l-neiliciency in the system, which maybe appreciated by considering the conditions when one intake. port is entirely closed and the other wide open. Under such conditions the pressure in the line connected to the closed port will be' substantially .atmospheric pressure, while the pressure on the line connected to the open port will never equal the pump negative pressure on account of the leak, but willalways be above the pump pressure. This loss averages about 50% `of the pump pressure,

varying theamount of leak inversely with the amount of opening of the`plck-oi-valve so that the` leak is substantiallyr entirely cut off when the pick-off valve is wide open. This is preferably done -by employing an extra valve reversely moved Withrespect to the normaLpick-off valve and which closes a leak port as the corresponding pick-off port is opened and vice versa.

Referring to the drawings, showing several -forms my invention may assume:

Fig. 1 shows my invention as applied tothe gyro vertical of an .automatic pilot, showing it applied both to the rotary type and piston type et pick-01T valve, many of the parts being in horizontal section.

Fig. 2 shows a vertical transverse section of the rotary valve taken on line 2 2 of Fig. 3.

Fig. 3 is a horizontal section of the same taken atright-angles to Fig. 1, and on line 3-3 of Fig. 2.

varying between 1'5 and85%, depending upon the type of ports, passages and leaks.

From the foregoing analysis it will be evident that to attain as useful di-ierential pressure all of the negative pressure produced by -the pump, there should be no leak in the side of the line connected to the pump'when the valve is wide open, and preferably that the leak shouldl be reduced as the port is being opened.

Fig. 4 is a perspective view of the double rotary valve proper or cut-off member. f

Fig. .5 is a diagram showing the improved efliciency secured by my invention. y

I have shown my invention as applied to a standard gyroscoplc horizon or gyro vertical, en-

closed within a casing 1, from which air is normally continuously pumped through a pipe 2.-

described in the prior patent to B.-G. Carlson No.'

1,982,636, datedDecember 4, 1934, forAir driven gyro verticals. Said bar is moved up and down on pitching vof the craft, by a crank pin Il on I trunnion `5 on the rotor casing, extending through the gimbal ring, while the said bar, being pivoted by a pin l2 on the gimbal ringrocks laterally therewith on roll or bank of the craft.

The bankingpick-oif valve is shownas in the form of a. semlcircular cut oi member or segment I3 or half cylinder mountedon a shaft I4 journaled at the vrear and outside of the casing I in bearings l! and 2D, and which is turned from One`-of the principal purposes of my invention 5.5

the gyroscopeby means of a gear l5 on shaft I4 meshing with a gear I6 secured to the hub or extension I1 from the gimbal ring 3. Said segment I3 is enclosed in a housing or valve casing I3 which is also rotatably mounted about the axis of shaft Il, as by means of bearing I9 and 2l.

I preferably incorporate in the same casing I8 my new cut-off valve 22 for the leaks or bleed holes. The inner valve structure therefore assumes the appearance shown in Fig. 4, consisting of two adjoining half cylinders, one cooperating with the opposed pick-off ports 23, 24 in the far end of the casing I3, and the other cooperating with the opposed leak ports 23 and 23 in the near end oi.' the casing. The far end of the casing is at all times connected to the vacuum pump through port 21 and pipe 21', while the other part of this chamber is at all times connected-to the atmosphere through the leak port 23 and. if desired, pipe 23', the chamber being separated into two parts by the central circular portion 33 of the rotary valve. The main pickof! -ports 23 and 23 lead through pipes 23 and 24' to some form of diierential pressure servo device. In their normal position, the ports 2l and 23 are =both bisected by the main portion of the valve Prom an inspection of Figs. 1, 2 and 3 it will beseen that eachprimaryport 23 and 2| is connected in series with a bleed port 25, 23, respectively, through the pipe connections 23', 23',

thereby furnishing two parallel paths for the air iiow between the continuously open intake port 23 and the continuously open outflow port 21. Each of said passages is tapped by the pipes 23' and 24', transmitting the static pressure in the respective passages to the valve chambers -23 and 33, respectively. No appreciable air flow occurs, therefore. Athrough the valve chambers 23 and 33, but the pressure in each follows closely the static pressure of the air flowing through the passagesn and 23', respectively, which in turn depends on the relative opening of the two pairs of ports in series 23, 23 and 2l, 23. In order to build up the effective pressure, the servo device includes a relay valve 3l, having opposite air pressure chambers 23 and 33. I'he bleeds therefor are provided in said pipes 23 and 24' by the pipes 23', 23' tapped into pipes 23', 24', re-

said port is wide open. The rate of change of pressure dp/dt (sensitivity) is also materially increased. It will be understood that the main servo motor 33 is operated preferably hydraulically from the relay valve 3l, the former controlling the control surface or surfaces 33, in this instance the ailerons. A My invention is likewise applicable to the piston type of pick-off device shown operating about the -foreand aft axis of the plane in Fig. 1. Ac-

cording to this form, a double piston valve 31, 31'y is connected through a piston rod 38 to a rocker arm 33 secured to a shaft 43 pivoted on the gimbal ring 3, said shaft being rocked from an arm 4I rocked from the movement of the lever 42 carrying the horizon bar 3', the arrangement being shown more in detail in the aforesaid patent of Kenyon and Zand. Surrounding the double piston 31, 31' is a sleeve 43 which is adjustable from the follow-back chamber 32' slmilar to device 32. Said sleeve is provided not only with the main pick-of! ports I3 and 41 and with the :main pumpport I3, but also withbleed -ports 43 and 53 located on opposite sides of the pistons 31 and 31' from the main ports I3, 41. H ence, itwiilbeseenthatasoneofthemain ports is closed, the corresponding bleed will be opened. and vice versa. I have also shown ex- `haust ports 5I connected with the atmosphere.

It will be understood that the several ports in sleeve 43 extend through the same and are enlargedattheirouterendssoastoremainunder the proper ports in the housing I5 regardless of the slight movement of the sleeve under the follow-back iniiuence of the chamber 32'.

'Ihe improved eillciency secured by my invention is graphically shown in Fig. 5 wherein the abscissas are plotted in both directions from aero spectively, and connected to the 4'leak ports 23, 23.

" The follow-back pressure device 32 also has its tvo sides connected to the pipes 23', 24' and the connected leak `pipes through pipes 33, 34, so that the leak ports 2l, 23 serve both the main relay valve 3l and the yfollow-baci: chamber 32.

- being opened,.so that maximum efficiency. is setimes,

the leak oonn'e'oted'tothe and represent degree of displacement of the pickon valve member I3, while the-ordinates represent percentage of effective differential pressure (i. e. the applied vacuum) from zero to. 100. The curves A and A show a typical example of efi'iciency for the ordinary type pick-of! valve, while curves B Iand B' show the eiliciency for my improved type of valve with the cut-oi! forthe bleed openings as weil as the pick-oft openings.

As many changes could be made in the above construction and many apparently widely difierent embodiments o f this invention could be made without departing from the scope thereof, it is intended that all matter contained in the above description or shown'in the accompanying drawings shall be interpreted as illustrative and not in alimitingsense.

'ports adjacent opposite ends thereof. means for continuously withdrawing air from the end thereof containing the 1pick-offV ports, a leak to 4the 'atmosphere continuously connected t0 the other end'thereof. an inner relativelymovable double acting cut-oil member separating said two ends and normally acting to partially and equally close all said ports, one of which members is con'-y nected to the sensitive element to be turned.

thereby, a differential pressure servo device connected with each pick-0I! port. the aforesaid,

bleed ports being respectively connected between the proper pick-olf port and said device. 'and said pick-on member upon initial displacement in one direction operating to increase the' opening-of one entireiycloeedatthetimeilpickwIl-portmddecreuetheopeningoftbe crease the opening ci the bleed port connected to the iirst pick-off port and to increase the opening of the bleed port connected to the second pickoff port.

2. In a pick-off valve of the differential air flow type for sensitive elements, a double semi-cylindrical rotary Valve turned from said element, a ported chamber therefor having a pair of pick,- off ports and a continuously open pump port in' one end and a pair of bleed ports and a continuously open port connected to the atmosphere in the other end, said valve separating the two ends of said chamber, and pipes connecting a servo device to said pick-off ports, said bleed ports being connected in said pipes, s'o constructed and arranged that as one pick-ofi port is being opened and the other closed, the bleed port connected to the former is being closed and the other bleed port is being opened.

3. In a pick-cifrotary valve of the diierential air flow type for sensitive elements, an outer enclosing member having pick-off ports, means for maintaining said member at a pressure diierent from atmospheric pressure, an inner relatively turnable cut-oi member, one of which members is connected tothe sensitive element to be turned thereby, a differential pressure follow-back device connected with each port and also coupled with the other of said members to turn the same, a differential pressure servo device connected with each port, leaks between each port and said devices to supply air flow, and additional valve lmeans operated from said element for cutting on tion, a pair of ports-in said casing adjacent the two edges of each of said surfaces so as to be normally partially open an equal amount, whereby as one port is being opened the other port is being closed, `and a port at each end of said casing beyond said valve, oneof which is adapted to be connected to an air pump and the other to the atmosphere. V

5. In a differential air' flow `rotary valve for sensitive elements, a casing having a cylindrical chamber therein, a relatively rotary valve thereby as one port is being opened the other port is being closed, and a port adjacent each end of said i casing, both of whih remain open during the normal operation of the valve, and one of which remains connected to an air tothe atmosphere.

6. A rotary pick-off valve for a sensitive device such as a gyroscope, by means of which the said valve produces a differential air pressure to conpump and the other trol a servo device, comprising a cylindrical valve4 chamber partitioned into two axially separated compartments, two channels connecting each of two circumferentially spaced ports in the wall of oneof said compartments to respective circum-` channel and to simultaneously further close a port at the end of said channel throughout substantial rotational movements of said valve,` a pair of pipesl connected to said ktwo channels adapted to transmit the static pressure therein to the servo device, and an additional port in each ofsaid compartments which remains open during all normal positions of said valve and which ports are connected to sources of different air pressure, whereby a variable flow of air is main- .mitting said pressure diierences through said pipes to the servo device.4

7. A rotary pick-01T valve of the diierential air pressure typefor controlling a servo device within spaced at both ends from the ends of said chamber and dividing the chamber into two parts,

said valve having one end formed as a segmental i cylinder with itsplane surface facing in one direction,` andthe other end similarly formed but with its plane surface facing in a diierent diport and to close the low pressure port of the i rection, apeir of ports in said casing adjacent member inside said chamber and rotatable with respect thereto and adapted to gradually simultaneously close the high pressure port and open the low pressure port of one channel and simultaneously to gradually open the high pressure other channel through substantial angular movements of the valve, an air pressure responsive servodevice, and means for transmitting thereto the differential static air pressure existing in said two chambers.

WILLIAM M. HARCUM. 

